The heat transfer analysis and optimal design on borehole ground heat exchangers

Abstract

The paper makes heat transfer analysis on borehole ground heat exchangers (GHEs) of ground-coupled heat pump system, for one thing, the thermal transmission on two cases including sing U-T ube and double U-T ubes inside borehole are illustrated, for another, the heat transfer characteristics outside borehole are presented based on the mathematical model, it is meaningful to obtain the analytical solution of temperature response in the underground medium. The relevant analysis lays a firm foundation for the optimal design of borehole GHEs because it can provide theoretical guidance for the calculation and design. In addition, some factors which can exert influences on the heat exchange performance of GHEs are pointed out, such as the arrangement of boreholes GHEs, the type of circulating liquid and so on. Afterwards the impacts degrees of these factors are studied according to simulation. It is necessary to optimize the design of borehole GHEs because in such a way can the size of GHEs be reduced so that the initial cost of the system is lowered, this is favourable for the application of ground-coupled heat pump technology.